Does your preheating take longer than specified in the cutting table?
Is the cutting quality bad?
One reason may be the incorrect setting of the flame.
A cutting flame should have the correct mixture between heating oxygen and heating gas.
With propane, it is approx. 1 part propane and 4 parts oxygen. For acetylene, it is about 1:1.
In the attached video, you can see examples of a heating flame.
For the correct adjustment often years of experience is necessary.
Alternatively, you use APC, our fully automatic Oxy-Fuel Process Control System.